Composition for producing a polymer, a method for producing the polymer, said polymer, use of the polymer, and an electrically dimmable glazing enclosing the polymer

ABSTRACT

The present invention relates to a composition for producing a polymer, comprising: a) from 20 to 60% by weight, based on the entire composition, of at least one monomer; and b) from 30 to 60% by weight, based on the entire composition, of at least one branched pre-polymer, wherein the composition is liquid at room temperature and under normal pressure; use of the composition, a method for producing a polymer using the composition, as well as an electrically dimmable glazing that encloses the polymer.

The present invention relates to a composition for producing a polymer,a method for producing the polymer using the composition, said polymer,the use of the polymer, and an electrically dimmable glazing thatencloses the polymer

The curing of monomers and their mixtures (polymerization) is generallyassociated with a volume contraction or an increase in material density.These changes increasingly lead to stresses in the material and,especially in the case of laminated glass, can result in end productswith defects or areas of inadequate adhesion. In order to solve thisproblem, the polymerization shrinkage during curing must be reduced.

By way of example, the following table lists literature data on thevolume shrinkage of a few selected typical monomers.

Monomer Volume shrinkage [%] Methyl methacrylate^([1]) 23% Ethylmethacrylate^([1]) 22% n-Propyl methacrylate^([1]) 21% n-Butylmethacrylate^([1]) 23% Isobutyl methacrylate^([1]) 21%Methylacrylate^([1]) 23% Ethyl acrylate^([1]) 21% Vinyl chloride^([2])34% Acrylonitrile^([2]) 31% Vinyl acetate^([2]) 21% Styrene^([2]) 15%

One common method for reducing shrinkage is to introduce fillers, suchas silica (SiO₂) particles^([3]) The filler volume limits the shrinkageduring the polymerization. However, this method alters the physicalproperties of the resulting polymer, such as hardness and flexibility.Likewise, the viscosity of the mixture increases unfavorably.Furthermore, the addition of coarse-grained fillers increases the wearof the production machines, resulting in an increase in productioncosts.

Thus, the shrinkage can be reduced by addition of silica particles to2.2 to 8.8%^([3]).

According to the prior art, an alternative method of reducing shrinkageis to add pre-polymers to the monomer mixture. Pre-polymers consistlargely of linear oligomers or polymers of the monomer to be cured,which can increase the density of the monomer mixture and thus reduceshrinkage after polymerization. The greater the proportion ofpre-polymer selected, the less the shrinkage. However, as the molecularweight of the pre-polymer increases, the viscosity of the monomermixture also increases unfavorably. This leads to problems in thetransport of the mixture and, in extreme cases, can lead to gelation,severely limited processability, and, in extreme cases, to damage ofproduction facilities. The resulting high and thus disadvantageousviscosity of the pre-polymers make it ultimately impossible in practiceto use a pre-polymerizate with the usual filling methods used on anindustrial scale. Thus, for example, a high-viscosity resin can nolonger be pumped through small cannulas in the space between two glassplates.

Another method, which is often used to reduce the polymer shrinkageaccording to the prior art, is the use of so-called “expandingmonomers.”^([4]) These often consist of ring systems which are processedby ring-opening polymerization. The advantage of this method is that theresulting polymer chains have a larger volume than the monomers, whichin theory results in a positive shrinkage (expansion) of the curedpolymer. However, this requires special monomers, which have to beindividually adapted to the field of application and thus can beobtained only with difficulty. The method of “expanding monomers” istherefore not a widely used method and it is tied to the chemicalproperties of the monomers and the resulting polymers. Polyacrylates andpolystyrene cannot be prepared by the above methodology.

Another approach for reducing the shrinkage of a monomer mixture between2 glass sheets consists of partially curing the monomer mixture. Aftershort-term curing, a cast resin mixture was injected repeatedly betweenthe glass sheets and then completely cured. This method reduces thestresses in the material and prevents the film from detaching from theglass surface. In this case, however, there is a significant addedexpense since this partial curing cannot be automated and involves highcosts.

In view of the problems known from the prior art, it is the object ofthe present invention to provide a composition for producing a polymerwhich overcomes the disadvantages of the prior art, in particular has areduced reduction of the volume (=shrinkage, or polymerization shrinkageor volume shrinkage) with as constant as possible low viscosity duringthe transition from a liquid monomer mixture (=composition) to the curedpolymer (=polymer). It is also intended to provide a composition formaking a polymer, wherein the properties of the polymer do not changesignificantly during curing (polymerizing).

It is also the object of the present invention to provide a polymerwhich overcomes the disadvantages of the prior art. It is also intendedto provide a method of producing the polymer as well as productscomprising the polymer which overcome the disadvantages of the priorart.

This object is achieved by a composition for producing a polymercomprising: a) from 20 to 60% by weight, based on the entirecomposition, of at least one monomer; and b) from 30 to 60% by weight,based on the entire composition, of at least one branched pre-polymer,wherein the composition is liquid at room temperature and under normalpressure.

For the purposes of the invention, a polymer is a chemical substancewhich consists of macromolecules. The macromolecules of the polymer arecomposed of several (or many) structural units called monomers, whichare connected to each other by covalent bonding.

For the purposes of the invention, a monomer is a low molecular weight,reactive molecule which is suitable for the construction of a polymer bycombination with other monomers. According to the invention, unlessotherwise stated in the application, a monomer has at least onefunctional group. A functional group here is a group that allows thepolymerization of the monomer. Particularly preferred here is a C═Cdouble bond as a functional group, by which a radical chainpolymerization is made possible. By way of example, the C═C double bondof a vinyl group or the corresponding C═C double bond of an (alkyl)acrylate group may be mentioned in this connection.

For the purposes of the invention, the term pre-polymer denotes areactive oligomer which is used to prepare polymers. In one embodiment,it may be provided that the pre-polymer is a branched pre-polymer. Thebranched pre-polymer comprises at least one, preferably several, sidechain(s). In a further embodiment it can be provided that the monomersand pre-polymers contained in the composition according to the inventionare radically polymerizable, that is, they comprise radicallypolymerizable units. In other words, it can be provided that thecomposition according to the invention is one for producing a polymer bymeans of radical polymerization. It can be provided that the compositionis used for the preparation of polyacrylates, polymethacrylates,polystyrenes, or copolymers thereof.

For the purposes of the invention, the term room temperature denotes atemperature of 20° C. The term normal pressure refers to a pressure of1.01325 bar.

According to the invention, it may further be provided that thecomposition according to the invention comprises further constituents,for example a polymerization initiator, for example Ergacure 819, asolvent, for example propylene carbonate, or further additives, forexample lithium perchlorate.

In addition, it can be provided that the composition according to theinvention contains radically polymerizable crosslinkers, for examplediacrylates, triacrylates, tetraacrylates, or similar compounds.

According to the invention, it is provided that the constituentscontained in the composition according to the invention add up to atotal amount of 100%.

It is preferably provided that the monomer is contained in an amount of25 to 55% by weight, particularly preferably 29 to 50% by weight, basedon the entire composition, in the composition. It is likewise preferablethat the branched pre-polymer is contained in the composition in anamount of 35 to 55% by weight, more preferably 35 to 50% by weight,based on the entire composition. The use of the preferred amount (s) ofmonomer and/or pre-polymer results in a particularly low viscosity.

It is likewise preferable that the branched pre-polymer has a numberaverage molecular weight Mn of 1,000 to 10,000 g/mol, preferably 1,500to 8,000 g/mol.

In addition, it is preferable that the branched pre-polymer has a weightaverage molecular weight Mw of 2,000 to 40,000 g/mol, preferably 4,000to 30,000 g/mol.

It is also preferred that the pre-polymer has a dispersity of from 2 to10, preferably from 2.5 to 8. The term dispersity here describes theratio of weight average of the molecular weight to the number average ofthe molecular weight.

Due to the preferred choice of the number average molecular weightand/or the weight average molecular weight and/or the dispersity of thebranched pre-polymer, a particularly low shrinkage could be achieved.The lowest shrinkage could be achieved by combining the preferredfeatures.

It can likewise be provided that the pre-polymer has a degree ofbranching of 0.4 to 0.7, in another embodiment, from 0.5 to 0.6.

Both the number average molecular weight and the weight averagemolecular weight were determined by size exclusion chromatography (SEC).For the SEC measurements, an Agilent 1200 system with a G1310A pump, aG1362A refractive index detector, and PSS Gram30 and PSS Gram1000columns connected in series, with a separability of 374-1.040.000 Da wasused. The solvent used was a mixture of N, N-dimethylacetamide (DMAc)and 5 mmol of LiCl. The flow rate was 1 mL min-1 and the column oven wasset at a temperature of 40° C. The system was calibrated with polymethylmethacrylate and polystyrene standards.

Further, the composition of the present invention and the polymerprepared based on the composition were characterized by nuclear magneticresonance (NMR) spectroscopy. For all 1H NMR spectra recorded, a 300 MHzBruker Fourier300 Avance spectrometer was used at room temperature. Thechemical shift (in ppm, parts per million) was shown based on thesolvent signal. The solvent used was deuterated chloroform,tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO) from the companyDeutero.

In addition, it is preferred that the monomer is selected from thegroup, consisting of methyl methacrylate, ethyl methacrylate, n-propylmethacrylate, n-butyl methacrylate, isobutyl methacrylate, methylacrylate, ethyl acrylate, vinyl chloride, acrylonitrile, vinyl acetate,styrene, 2-ethylhexyl acrylate, hydroxyethyl acrylate, N-Isopropylacrylamide, N, N-dimethylaminoethyl methacrylate, N,N-dimethylaminoethylacrylate, 2-vinylpyridine, 4-vinylpyridine or mixtures thereof,preferably n-butyl acrylate and/or 2-ethylhexyl acrylate and/or2-hydroxyethyl acrylate and/or styrene. For the preferred monomers, aparticularly advantageous relationship between low shrinkage and lowviscosity could be observed.

Moreover, it is preferred that the branched pre-polymer is a branchedpoly(alkyl)acrylate, preferably branched poly-n-butyl acrylate, branchedpoly-2-ethylhexyl acrylate, branched poly(n-butylacrylate-co-2-ethylhexyl acrylate), or mixtures thereof, branchedpolyacrylate, branched polystyrene, or a mixture thereof. By choosingthe pre-polymers described as preferred, low shrinkage properties couldbe observed with simultaneously low viscosity.

In a further embodiment, it can be provided that the pre-polymersaccording to the invention are those pre-polymers which can be preparedfrom the monomers mentioned above as being preferred (and/or similarmonomers).

It is preferred that the composition further comprises c) from 0.1 to 2%by weight, based on the total composition, of a further monomer havingat least two polymerizable groups. By adding such a further monomer,which comprises a plurality of functional groups, that is to say groupswhich allow polymerization, the degree of branching of the polymer couldbe increased and therefore the curing of the polymer could be increased.In this preferred embodiment, in which another monomer, having aplurality of functional groups, is contained in the composition, it maybe preferable provided that the monomer, contained in an amount of from20 to 60% by weight, based on the entire composition in which thecomposition, has exactly one functional group.

It is further preferred that the pre-polymer is obtainable by reacting(a) at least one monomer having a polymerizable group; (b) at least onemonomer having at least two polymerizable groups; and (c) at least onechain transfer agent.

In this context, it is preferable that reacting the monomer having apolymerizable group, the monomer having at least two polymerizablegroups, and the chain transfer agent is carried out in the presence of apolymerization initiator.

Particularly preferred here is that the monomer having a polymerizablegroup (a), the monomer having at least two polymerizable groups (b) andthe chain transfer agent (c) are present in a ratio of (a)=1 to 100,preferably (a)=2 to 70/(b)=1/(c)=0.1 to 10, preferably (c)=0.5 to 6. Theratio here refers to the substance amounts. The (substance amount) ratioa/b/c is therefore preferably 1-100/1/0.1-10.

It can be provided according to the invention that reacting the reagentsfor producing the pre-polymer takes place in the presence of furtherconstituents, for example in the presence of a solvent of apolymerization initiator, for example Irgacure 819, etc.

Irgacure 819 here describes the mixture of the corresponding trade namemarketed on the filing date.

A chain transfer agent according to the invention is a compound whichhas at least one weak bond, by means of which a chain transfer reactionis facilitated. Chain transfer agents preferred according to theinvention are aliphatic thiols and/or aromatic thiols. Particularlypreferred here is the use of dodecanethiol as a chain transfer agent.

The described preferred preparation of the pre-polymer describes theso-called “Strathclyde” method. Here, monomers having a functional group(such as divinyl monomers) and monomers having two (or more) functionalgroups (such as divinyl monomers) are reacted in the presence of a chaintransfer agent. By adding an amount of the chain transfer agent, thelength of the primary polymer chain can be controlled. As a result,complete curing of the mixture is prevented.

The object underlying the invention is further achieved by the use ofthe composition according to the invention for producing a dentalcomposite, for producing a glass ionomer cement, for producing alow-shrink acrylate adhesive, for producing a low-shrink acrylic glasssheet, for producing a precisely fitting acrylic materials, inelectrical engineering, or for producing a glass-polymer-glass compositepane, preferably by means of cast resin technology.

Further, the object underlying the invention is achieved by a method forproducing a polymer, the method comprising: a) providing a compositionaccording to the invention; and b) reacting the monomer and thepre-polymer.

In this case, it can be provided according to the invention that thereaction of monomer and pre-polymer takes place in the presence offurther constituents, for example a solvent, of a polymerizationinitiator, for example Ergacure 819, etc.

Finally, the object underlying the invention is achieved by anelectrically dimmable glazing, comprising a polymer obtainable by theprocess according to the invention.

Electrically dimmable glazings are suitable for regulating andcontrolling the flow of energy from the outside into a building. Here,an electrical pulse, for example in the form of a suitable voltage, isused to change the glazing in its photometric properties, for example,lowering the light transmission from high values (e.g. 60%) to lowvalues (e.g. 10%) (=coloring) during strong irradiance and increasingthe light transmission from low values (for example 10%) to high levels(for example 60%) (=decolorization) during weak irradiance.

An electrochromic element, which is used for production in anelectrically dimmable glazing, usually consists of two transparenttabular materials (glass or plastic, e.g. Plexiglas or polycarbonate),which are bonded (glued) to each other via an ion-conductive film.Between the ion-conductive film and the adjacent surfaces of thetransparent panels, there are conductive (TCO=transparent conductiveoxides) and electrochromic coatings (EC 1 and EC 2) in the followingarrangement:

-   -   glass-TCO-EC 1-ion-conductive film-EC 2-TCO-Glass

Materials for conductive transparent coatings (TCOs) may be the knownsystems: fluorine doped tin oxide (e.g. PILKINGTON K-GlasN or PILKINGTONTEC glass), ITO (indium tin oxide), ATO (antimony tin oxide), or others(e.g. B. aluminum doped zinc oxide).

Materials for the electrochromic coating (EC 1) may be: tungsten oxide,molybdenum oxide, nickel oxide, iridium oxide, or mixtures of said metaloxides.

Materials for the electrochromic coating (EC 2) may be: cerium oxide,titanium oxide, vanadium oxide, niobium oxide, tantalum oxide, ormixtures of said metal oxides.

The core of such a reversibly switchable electrochromic element is anion-conductive polymer, which is located between the two coated panelsand thus permanently bonds them. The ion-conductive polymer additionallyhas the function of providing charge carriers in order to transportcharge carriers from one electrochromic coating (e.g. EC1) to the otherelectrochromic coating (e.g.EC2) by means of an electrical voltagepulse. Suitable charge carriers can lithium ions and hydrogen ions.

Such an ion-conductive polymer is not available on the market as a film.For the preparation of an electrochromic element therefore, startingfrom a prepared mixture of all necessary components—the so-calledmonomer mixture—it is cast between two prepared glass plates and thencured by UV radiation. During hardening, i.e. from the transition of thelow-viscosity liquid phase of the monomer mixture to the solid polymerphase, the material shrinks. This volume shrinkage is considerable ataround 12% and leads to mechanical stresses in the glass-polymer-glasscomposite system, which can affect the corners and edges of the laminatein particular. The mechanical stresses can lead to mechanicaldetachments and thus to restrictions in use under stress of the windowelements (temperature fluctuations over the course of the day and theyear). According to previous findings, the mechanical stresses areparticularly strong in model disks (triangles, pentagons, trapeziums,etc.) with corner angles smaller than 90°.

Ion-conductive films can be prepared based on modified polyvinylbutyral, polyethylene oxides, polyethyleneimines, or polyacrylates.Modified polyvinyl butyral films are sufficiently described in patentsDE 103 27 517 and WO 02/40578 of GESIMAT Co., for example; modifiedpolyethylene oxide or polyethyleneimines are sufficiently described inpatents FR 2690536, U.S. Pat. No. 5,241,411 and DE 69213833 of theSaint-Gobain Co. Acrylates and other polymers are known from EP 1 283436 of BASF AG as well as DE 695 28 148 and DE 44 17 219 of FLACHGLASAG/FLABEG/EControl glass and EP 2093 270 of EControl glass.Ion-conductive films are often referred to in the literature aspolymeric ionic conductors. Both names (“ion-conductive film” and“polymeric ionic conductor”) are equivalent and synonymous.

Example 1 according to the invention is an example of a polymeric ionconductor which is suitable for an ion-conductive film for theproduction of switchable glasses according to the abovementionedstructure.

The present invention relates to the production and use of a resinwhich, on transition from the liquid monomer mixture to the curedpolymer, has a significantly lower shrinkage than that mentioned in theprior art and at the same time has a low viscosity.

Also disclosed in this invention is a new type of filler (pre-polymer)which does not appreciably affect the properties of the polymer aftercuring, but significantly reduces polymer shrinkage without unfavorablyincreasing the viscosity.

Surprisingly, it has been found by the inventors that the use of thecomposition according to the invention causes the reduction of polymershrinkage of a cast resin mixture during the curing process(polymerization). By adding branched pre-polymers, for examplepolyacrylates, which can be prepared by the “Strathclyde method”developed by Sherrington, the shrinkage of a cast resin mixture (monomermixture) can be considerably reduced. It should be noted that theviscosity of the cast resin mixture increases only slightly compared tolinear pre-polymers of comparable molecular weight.

The invention will be described in detail below on the basis ofparticularly preferred embodiments.

In order to reduce the polymer shrinkage of a polymer during curing(transition of the liquid low viscosity phase of the monomer mixture tothe solid polymer phase), branched pre-polymers are added. Thesebranched polymers are prepared by the “Strathclyde” method developed bySherrington.^([5]) Here monomers with (meth)acrylic or vinyl groups andpolyfunctionalized crosslinkers (also with (meth)acrylic or vinylgroups) are copolymerized. So as to prevent gelation, an aliphatic thiol(R₄—SH with R₄=aliphatic) or an aromatic thiol (R₄—SH mit R₄=aromatic)is added to the monomer mixture. By varying the components such as thethiol, for example, the molecular weight of the resulting branchedpolymer can be adjusted.

The branched polymers thus produced are now added as additives in theproduction of polymeric materials. If branched polymers are now used(prepared for example from n-butyl acrylate according to the Strathclydemethod) in admixture with monomeric n-butyl acrylate, the volumeshrinkage during polymerization can be lowered to 4%, while the volumeshrinkage in pure n-butyl acrylate is about 11% (see Example 1).

The viscosity of the monomer mixture is not increased as much when usingbranched polymers as compared with the use of linear pre-polymers. Thisis due to the form factor α. The viscosity of a polymer solution isdescribed by the Mark-Houwink equation.(η=KM ^(a)).

Here η describes the viscosity of the polymer solution, and M the molarmass of the dissolved polymer. K is a substance-specific factor, just asa is the polymer-specific form factor. For linear polymers this formfactor is 0.72. Branched polymers, on the other hand, have a lower formfactor, depending on the degree of branching. This leads to a reductionin the viscosity when adding branched polymers in contrast to linearpolymers with the same molecular weight. Thus, the monomer mixture usedalso has a lower viscosity compared with the conventionally used linearpre-polymers.

An essential aspect of the invention is therefore the use of branchedpre-polymers as additives in monomeric mixtures for the reduction of thepolymer shrinkage, wherein, at the same time, by the use of the branchedpre-polymers, only a slight increase in viscosity occurs, which allowsthe processing and flowability of the resin.

One meaningful example that might be mentioned is the smaller increaseof linearly polymerized polystyrene compared with the branchedpolymerized styrene^([6]). This is shown in FIG. 1. FIG. 1 shows theintrinsic viscosity as a function of the molar mass of the polymers. Itis noticeable that the curve of the linear polystyrene increases morestrongly in comparison to the branched polystyrene.

FIG. 1: Difference in the viscosity increase of linear and branchedpolystyrene as a function of the molar mass; (L-PS=linearly polymerizedpolystyrene, HBPS=branched polymerized polystyrene)

In summary, this invention has the following advantages: The volumeshrinkage of a monomeric mixture during curing is significantly reduced.

The viscosity of the resin mixture remains low and can thus be used andpumped on an industrial scale.

The invention will be illustrated below in an exemplary manner withreference to specific examples. These examples are illustrative of theinvention and do not limit the scope of the invention as recited.

EXEMPLARY EMBODIMENTS

The following exemplary embodiments are mentioned.

Examples 1-3: Preparation of a branched polyacrylate from a puremonomer, for example, n-butyl acrylate; preparation of a polymer filmwith the branched polyacrylate and the same monomeric acrylate

Examples 4-6: Preparation of a branched polyacrylate from a puremonomer, for example, 2-ethylhexyl acrylate; preparation of a polymerfilm with the branched poly-2-ethylhexyl acrylate and another monomericacrylate, for example n-butyl acrylate.

Examples 7-9: Preparation of a branched polyacrylate from a pure monomerfor example, n-butyl acrylate; preparation of a film with the branchedpoly(n-butyl acrylate) or poly(ethyl hexyl acrylate) and a mixture ofdifferent monomeric acrylates, for example, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxy ethyl acrylate.

Examples 10-11: Preparation of a branched acrylate copolymer fromvarious monomers, e.g. n-butyl acrylate and 2-ethylhexyl acrylate;preparation of a film with the branched poly (n-butylacrylate-co-2-ethyl hexyl acrylate) and another monomeric acrylate, forexample n-butyl acrylate

Examples 12-14: Preparation of a branched acrylate copolymer fromvarious monomers, e.g. n-butyl acrylate and 2-ethylhexyl acrylate;preparation of a film with the branched poly(n-butyl acrylate-co-2-ethylhexyl acrylate) and a mixture of different monomeric acrylates, forexample, n-butyl acrylate, ethyl hexyl acrylate, 2-hydroxy ethylacrylate.

Meanings are always the same:

-   -   nBA n-butylacrylate    -   EHA 2-ethylhexylacrylat    -   HEA hydroxyethyl acrylate    -   BDDA butanediol diacrylate    -   DDT dodecanethiol    -   TPGDA tripropylene glycol diacrylate    -   DVB divinyl benzene    -   THF tetrahydrofuran

Example 1: Preparation of a Poly(n-Butyl Acrylate) (PnBA) Film

The used branched PnBA was prepared as follows. 3 kg nBA were mixed with117 g of tripropylene glycol diacrylate (TPGDA), 395 g of dodecanethiol(DDT), and 1.6 g of Irgacure 819. After 15 minutes of degassing/purgingwith argon, the mixture was irradiated for 20 minutes with a 100 W Hg UVlamp. The obtained branched polymer had a purity of 76% (nBA), amolecular weight distribution of M_(n)=1500 g/mol; Mw=4000 g/mol and adispersity of 2.51.

For the preparation of an ion-conductive polymer film for use in anelectrochromic element, a cast resin mixture of 29.05% nBA, 54.65%branched PnBA, 13.4% propylene carbonate, 1.50% lithium perchlorate(anhydride), 1% 1.4-Butane diol diacrylate and 0.4% Irgacure 819 wassubsequently produced. This cast resin mixture had a viscosity of 9.6mPas. After curing the film for 30 min under UV irradiation, a shrinkageof 4% could be determined. A similar mixture without addition ofbranched PnBA has a viscosity of 1.1 mPas and a shrinkage after completecuring of 11%.

Example 2: Preparation of a Poly(Ethyl Hexyl Acrylate) (PEHA) Film

The used branched PEHA was prepared as follows. 10 g EHA was mixed with6.7 g tripropylene glycol diacrylate (TPGDA), 22.9 g dodecanethiol (DDT)and 95 mg Irgacure 819. After 15 minutes of degassing with argon, themixture was irradiated for 20 minutes with a 100 W Hg UV lamp. Theobtained branched polymer had a purity of 85% (15% unreacted EHA) and amolecular weight distribution of Mn=7600 g/mol; Mw=23200 g/mol, and adispersity of 3. The obtained branched polymer had a purity of 85% (15%unreacted EHA) and a molecular weight distribution of M_(n)=7600 g/mol;M_(w)=23200 g/mol, and a dispersity of 3.

For the film preparation, a cast resin mixture of 49.4% EHA; 36.5%branched PEHA; 13.4% propylene carbonate, 0.3% butanediol diacrylate(BDDA), and 0.4% Irgacure 819 was subsequently produced. This cast resinmixture had a viscosity of 20 mPas. After curing the film for 30 minunder UV irradiation, a shrinkage of 5% could be determined. A similarmixture without the addition of the branched PEHA has a viscosity of 2mPas and a shrinkage after complete curing of 8%.

Example 3: Preparation of a Polystyrene (PS) Film

The used branched PS was produced as follows. 100 g of styrene with 2 gdivinyl benzene (DVB), 16.2 g dodecanethiol (DDT), and 67 mg Irgacure819 was dissolved in 50 mL of THF. After 15 minutes of degassing withargon, the mixture was irradiated for 20 minutes with a 100 W Hg UVlamp. The obtained branched polymer had a purity of 85% (15% unreactedEHA) and a molecular weight distribution of Mn=7600 g/mol; Mw=23200g/mol, and a dispersity of 3. The obtained branched polymer had a purityof 81% (19% unreacted styrene) and a molecular weight distribution ofM_(n)=3750 g/mol; M_(w)=29000 g/mol, and a dispersity of 7.8.

For the film preparation, a cast resin mixture of 35.9% styrene; 50%branched PS; 13.4% propylene carbonate, 0.3% divinyl benzene and 0.4%Irgacure 819 was subsequently produced. This cast resin mixture had aviscosity of 31 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 4% could be determined. A similar mixturewithout the addition of the branched PS has a viscosity of 2 mPas and ashrinkage after complete curing of 15%.

Example 4: Preparation of a Film from Mixtures

For film preparation, a cast resin mixture of 49.4% nBA; 36.5% branchedPEHA; 13.4% propylene carbonate, 0.3% butanediol diacrylate, and 0.4%Irgacure 819 was produced This cast resin mixture had a viscosity of 18mPas. After curing the film for 30 min under UV irradiation, a shrinkageof 6% could be determined. A similar mixture without the addition of thebranched PEHA has a viscosity of 1.1 mPas and a shrinkage after completecuring of 11%.

Example 5: Preparation of a Film from Mixtures

For the film preparation, a cast resin mixture of 49.4% EHA; 36.5%branched PnBA; 13.4% propylene carbonate. 0.3% butanediol diacrylate,and 0.4% Irgacure 819 was produced. This cast resin mixture had aviscosity of 20 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 4% could be determined. A similar mixturewithout addition of branched PnBA has a viscosity of 2 mPas and ashrinkage after complete curing of 8%.

Example 6: Preparation of a Film from Mixtures

For film preparation, a casting resin mixture of 35.9%2-hydroxyethylacrylate (HEA); 50% branched PnBA; 13.4% propylenecarbonate, 0.3% 1,4-butanediol diacrylate, and 0.4% Irgacure 819 wasproduced. This cast resin mixture had a viscosity of 41 mPas. Aftercuring the film for 30 min under UV irradiation, a shrinkage of 5% couldbe determined. A similar mixture without addition of branched PnBA has aviscosity of 6 mPas and a shrinkage after complete curing of 14%.

Example 7: Preparation of a Film from Mixtures

For the film preparation, a casting mixture of 30% nBA; 20% EHA; 35.9%branched PEHA; 13.4% propylene carbonate, 0.3% butanediol diacrylate,and 0.4% Irgacure 819 was produced. This cast resin mixture had aviscosity of 23 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 5% could be determined. A similar mixturewithout the addition of the branched PEHA has a viscosity of 1.8 mPasand a shrinkage after complete curing of 10%.

Example 8: Preparation of a Film from Mixtures

For the film preparation, a casting resin mixture of 30% nBA; 20% EHA;35.9% branched PnBA; 13.4% propylene carbonate, 0.3% butanedioldiacrylate, and 0.4% Irgacure 819 was produced. This cast resin mixturehad a viscosity of 21 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 6% could be determined. A similar mixturewithout the addition of the branched PEHA has a viscosity of 1.3 mPasand a shrinkage after complete curing of 11%.

Example 9: Preparation of a Film from Mixtures

For the film preparation, a casting resin mixture of 20% nBA; 20% EHA;10% 2-hydroxyethyl acrylate (HEA); 35.9% branched PnBA; 13.4% propylenecarbonate, 0.3% butanediol diacrylate, and 0.4% Irgacure 819 wasproduced. This cast resin mixture had a viscosity of 32 mPas. Aftercuring the film for 30 min under UV irradiation, a shrinkage of 7% couldbe determined. A similar mixture without addition of branched PnBA has aviscosity of 4.2 mPas and a shrinkage after complete curing of 13%.

Example 10: Preparation of a Film from Mixtures

The used branched copolymer (PnBA-co-PEHA) was produced as follows. 10 gnBA was mixed with 4.38 g EHA, 3.9 g tripropylene glycol diacrylate(TPGDA), 1.32 g dodecanethiol (DDT), and 5.4 mg Irgacure 819. After 15minutes of degassing with argon, the mixture was irradiated for 20minutes with a 100 W Hg UV lamp. The obtained branched polymer had apurity of 85% (15% unreacted EHA) and a molecular weight distribution ofMn=7600 g/mol; Mw=23200 g/mol, and a dispersity of 3. The obtainedbranched polymer had a purity of 81% (19% unreacted nBA and EHA) and amolecular weight distribution of M_(n)=2300 g/mol; M_(w)=6000 g/mol anddispersity of 2.6.

For the film preparation, a casting resin mixture of 50% 2-hydroxyethylacrylate (HEA); 35.9% branched PnBA-co-PEHA; 13.4% propylene carbonate,0.3% butanediol diacrylate, and 0.4% Irgacure 819 was produced. Thiscast resin mixture had a viscosity of 24 mPas. After curing the film for30 min under UV irradiation, a shrinkage of 7% could be determined. Asimilar mixture without addition of the branched PnBA-co-PEHA has aviscosity of 6 mPas and a shrinkage after complete curing of 14%.

Example 11: Preparation of a Film from Mixtures

For the film preparation, a casting resin mixture of 50% nBA; 35.9%branched PnBA-co-PEHA; 13.4% propylene carbonate, 0.3% butanedioldiacrylate, and 0.4% Irgacure 819 was produced. This cast resin mixturehad a viscosity of 19 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 6% could be determined. A similar mixturewithout addition of the branched PnBA-co-PEHA has a viscosity of 1.1mPas and a shrinkage after complete curing of 11%.

Example 12: Preparation of a Film from Mixtures

For the film preparation, a casting resin mixture of 30% nBA; 20% EHA;35.9% branched PnBA-co-PEHA; 13.4% propylene carbonate, 0.3% butanedioldiacrylate, and 0.4% Irgacure 819 was produced. This cast resin mixturehad a viscosity of 21 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 5% could be determined. A similar mixturewithout addition of the branched PnBA-co-PEHA has a viscosity of 1.8mPas and a shrinkage after complete curing of 10%.

Example 13: Preparation of a Film from Mixtures

For the film preparation, a casting resin mixture of 30% nBA; 20% EHA;35.9% branched PEHA-co-PnBA; 13.4% propylene carbonate, 0.3% butanedioldiacrylate, and 0.4% Irgacure 819 was produced. This cast resin mixturehad a viscosity of 27 mPas. After curing the film for 30 min under UVirradiation, a shrinkage of 6% could be determined. A similar mixturewithout addition of the branched PEHA-co-PnBA has a viscosity of 1.8mPas and a shrinkage after complete curing of 10%.

Example 14: Preparation of a Film from Mixtures

For the film preparation, a casting resin mixture of 20% nBA; 20% EHA;10% 2-hydroxyethyl acrylate (HEA); 35.9% branched PEHA-co-PnBA; 13.4%propylene carbonate, 0.3% butanediol diacrylate, and 0.4% Irgacure 819was produced. This cast resin mixture had a viscosity of 36 mPas. Aftercuring the film for 30 min under UV irradiation, a shrinkage of 7% couldbe determined. A similar mixture without addition of the branchedPEHA-co-PnBA has a viscosity of 4.2 mPas and a shrinkage after completecuring of 13%.

The invention can be used in all radical polymerizations in which theshrinkage during curing is to be reduced or avoided:

-   [1] S. Loshaek, T. G. Fox, J. Am. Chem. Soc. 1953, 75, 3544-3550.-   [2] F. S. Nichols, R. G. Flowers, Ind. Eng. Chem. 1950, 42, 292-295.-   [3] Versluis A., Douglas W. H., Cross M., S. R. L., J Dent Res 1996,    75, 871-878.-   [4] Bailey William J., E. Takeshi, Journal of Polymer Science:    Polymer Symposium 1978, 64, 17-26.-   [5] N. O'Brien, A. McKee, D. C. Sherrington, A. T. Slark, A.    Titterton, Polymer 2000, 41, 6027-6031.-   [6] S. B. Kharchenko, R. M. Kannan, J. J. Cernohous, Macromolecules    2003, 36, 399-406.

The features disclosed in the specification and claims may be relevantto the realization of embodiments both individually and in anycombination with each other.

The invention claimed is:
 1. A composition for producing a polymer,comprising: 20 to 60% by weight, based on the entire composition, of atleast one monomer; and 30 to 60% by weight, based on the entirecomposition, of at least one branched pre-polymer, wherein thecomposition is liquid at 20° C. and 1 bar; the at least one monomer isselected from the group consisting of methyl methacrylate, ethylmethacrylate, n-propyl methacrylate, n-butyl acrylate, n-butylmethacrylate, isobutyl methacrylate, methyl acrylate, ethyl acrylate,vinyl chloride, acrylonitrile, vinyl acetate, styrene, 2-ethylhexylacrylate, 2-hydroxyethyl acrylate, N-Isopropyl acrylamide, N,N-dimethylaminoethyl methacrylate, N, N-dimethylaminoethyl acrylate,2-vinylpyridine, 4-vinylpyridine, and any combination thereof; and thebranched pre-polymer is a reaction product of a) at least one monomerhaving one polymerizable group, b) at least one monomer having at leasttwo polymerizable groups, and c) at least one chain transfer agent. 2.The composition according to claim 1, wherein the at least one chaintransfer agent includes an aliphatic thiol, an aromatic thiol, or acombination thereof.
 3. The composition according to claim 1, whereinthe branched pre-polymer has a number average of the molar mass M_(n) of1,000 to 10,000 g/mol.
 4. The composition according to claim 1, whereinthe branched pre-polymer has a weight average of the molar mass M_(w) of2,000 to 40,000 g/mol.
 5. The composition according to claim 1, whereinthe pre-polymer has a dispersity of 2 to
 10. 6. The compositionaccording to claim 5, wherein the branched pre-polymer has a dispersityof 2.5 to
 8. 7. The composition of claim 1, wherein a viscosity of thecomposition is not greater than 41 mPas.
 8. The composition according toclaim 1, wherein the branched pre-polymer includes a branchedpoly(alkyl)acrylate, a branched polyacrylate, a branched polystyrene, ora combination thereof.
 9. The composition according to claim 8, whereinthe branched pre-polymer includes branched poly-n-butyl acrylate,branched poly-2-ethylhexyl acrylate, branched poly(n-butylacrylate-co-2-ethylhexyl acrylate), or any combination thereof.
 10. Thecomposition according to claim 1, wherein the monomer of the compositionincludes n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethylacrylate, styrene, or any combination thereof.
 11. The compositionaccording to claim 1, wherein the composition comprises a furthermonomer having at least two polymerizable groups in an amount of 0.1 to2% by weight based on the total weight of the composition.
 12. Thecomposition of claim 1, wherein the composition is adapted for producinga dental composite, a glass ionomer cement, an acrylate adhesive, anacrylic glass sheet, an acrylic material in electrical engineering, or aglass-polymer-glass composite pane.
 13. An electrically dimmable glazingcomprising the polymer of claim
 1. 14. A method of producing a polymer,comprising: forming a branched pre-polymer, wherein forming the branchedpre-polymer comprises reacting a) at least one monomer having onepolymerizable group, b) at least one monomer having at least twopolymerizable groups, and c) at least one chain transfer agent;preparing a composition comprising 30-60 wt % of the branchedpre-polymer and 20-60 wt % of at least one monomer, the monomer beingselected from the group consisting of methyl methacrylate, ethylmethacrylate, n-propyl methacrylate, n-butyl acrylate, n-butylmethacrylate, isobutyl methacrylate, methyl acrylate, ethyl acrylate,vinyl chloride, acrylonitrile, vinyl acetate, styrene, 2-ethylhexylacrylate, 2-hydroxyethyl acrylate, N-Isopropyl acryl; and reacting thecomposition to form the polymer.
 15. The method of claim 14, wherein ashrinkage of the composition after reacting the composition and formingthe polymer is not greater than 7%.
 16. The method of claim 14, whereina viscosity of the composition is not greater than 41 mPas.
 17. Themethod of claim 14, wherein a ratio for forming the branched pre-polymerof a) the at least one monomer having one polymerizable group to b) theat least one monomer having at least two polymerizable groups to c) theat least one chain transfer agent is 1-100/1/0.1-10.
 18. The methodaccording to claim 14, wherein the branched pre-polymer includes abranched poly(alkyl)acrylate, a branched polyacrylate, a branchedpolystyrene, or a combination thereof.